Effect of Bisphenol A on submerged-floating macrophytes and epiphytic biofilms

Bisphenol A (BPA), a representative environmental endocrine disruptor, is widely detected in aquatic systems, posing potential risks to ecosystems and human health. However, the effects of BPA on submerged-floating macrophytes and their epiphytic biofilms remain poorly understood. Two macrophytes were exposed to environmentally relevant concentrations of BPA to evaluate the interactions in aquatic plants. Results demonstrated that BPA exposure significantly inhibited the synthesis of photosynthetic pigments, reducing chlorophyll b content by 13.1 % and 12.2 % in Vallisneria natans (V. natans) and Spirodela polyrhiza (S. polyrhiza), respectively. Simultaneously, exposure to low-concentration BPA induced ROS generation rates of 4.79 μs^-1 kg^-1 in the S. polyrhiza monoculture group and 9.73 μs^-1 kg^-1 in the co-cultured submerged-floating macrophytes group, demonstrating enhanced ROS scavenging capacity in the co-culture system. Notably, compared to monoculture groups, antioxidant enzyme activities were significantly elevated in the co-cultured submerged-floating macrophytes group, improving plant tolerance to BPA stress. Scanning electron microscopy revealed that BPA altered the abundance of algae and bacteria in epiphytic biofilms and stimulated increased secretion of extracellular polymeric substances. Furthermore, microbial community analysis indicated that BPA reduced the diversity and richness of biofilm species, whereas co-cultivation significantly enriched the abundance of specific functional bacteria associated with degradation. Confocal laser scanning microscopy showed differential changes in polysaccharide and protein content within biofilms between monoculture and co-cultured groups under BPA exposure. Additionally, the increased content of quorum-sensing signaling molecules in plant biofilms suggests that BPA alters biofilm structure and function. These results reveal that BPA effectively activates defense mechanisms in submerged and floating macrophytes and profoundly influences the spatial structure of epiphytic biofilms. This study elucidates the effects of BPA on aquatic plants and provides a scientific basis for the application of aquatic plants and epiphytic biofilm systems in BPA bioremediation.